1. Field of the Invention
The present invention relates to a semiconductor device having an interlayer insulation film the required properties of which are liable to deteriorate by oxygen plasma treatment, and a process for producing the same. In particular, the present invention relates to a semiconductor device making it possible to restore deteriorated properties, and a process for producing the same.
2. Description of the Related Art
The demand for high-speed processing of signals in large scale integrated circuits (LSIs) has been increasing year by year. The speed of processing signals in LSIs is mainly decided by the operation speed of their transistors themselves and the delay time of signal-transmission in wiring. The operation speed of transistors, which has greatly influenced the speed of processing signals in the prior art, has been improved by scaling down the size of the transistors.
In LSIs having a designed size of less than 0.25 xcexcm, however, a decline in the signal-processing speed based on the delay in signal-transmission in wiring is becoming remarkable. Such an influence is high in LSI devices having a multilayer wiring structure wherein the number of wiring layers is over 4.
Recently, therefore, as a method for improving the delay in signal-transmission in wiring, there has been investigated a method of using, instead of an interlayer insulation film of conventional silicon oxide films, a hydrogen silsesquioxane (HSQ) film or the like, which has a smaller dielectric constant. The HSQ film is a resin film having a chemical structure wherein a part of Sixe2x80x94O bonds of a silicon oxide film is replaced by Sixe2x80x94H bonds. The film is applied onto a substrate and then heated and sintered so as to be used as an interlayer insulation film. Since almost all parts of the HSQ film are composed of Sixe2x80x94O bonds in the sane way as in conventional silicon oxide films, the HSQ film has a low dielectric constant and heat-resistance, up to about 500xc2x0 C.
However, when the HSQ film is used as an interlayer insulation film, there remains a problem that the HSQ film deteriorates in the step of exfoliating photoresist used for forming various patterns in usual lithographic technique and etching technique.
Generally, in the step of exfoliating photoresist, a treatment with oxygen plasma is conducted and subsequently remnants of the photoresist, which are not exfoliated, and etching remnants are removed. For this purpose, treatment with a wet exfoliating solution containing monoethanolamine or the like is conducted. When the HSQ film is exposed to oxygen plasma, Sixe2x80x94H bonds therein are broken and Sixe2x80x94OH bonds are generated so that the film comes to contain water. When the HSQ film is treated with the wet exfoliating solution, Sixe2x80x94H bonds are broken and Sixe2x80x94OH bonds are generated in the same way as in the treatment with oxygen plasma. That is, in these exfoliating steps, the HSQ film comes to contain a large amount of water. As a result, its dielectric constant unfavorably rises. If the HSQ film comes to contain a large amount of water, there arise a problem of leakage between vias. In the step of embedding in via holes by CVD or sputtering, the embedding in the via holes becomes insufficient by degassing.
The following will describe a process for producing a semiconductor device in the prior art. FIG. 1 is a cross section illustrating the semiconductor device producing process in the prior art.
An underlying layer 52 is first formed on a silicon substrate 51. The underlying layer 52 includes underlying layer elements such as transistors. Next, a barrier metal layer 53 is selectively formed on the underlying layer 52. Thereafter, a first metal wiring layer 54 is formed on the barrier metal layer 53. A reflection preventive layer 55 is formed on the first metal wiring layer 54. Next, a first silicon oxide film 57 is formed on the entire surface by plasma CVD. Subsequently, an HSQ film 58 is applied on the first silicon oxide film 57 by a coating machine. The resultant is subjected to provisional sintering on a hot plate, followed by sintering in a sintering furnace.
At this time, in order to prevent dissociation of Sixe2x80x94H bonds, nitrogen or the like is generally introduced into the space around the hot plate or in the sintering furnace so that the HSQ film does not react with oxygen or water. Next, a second silicon oxide film 59 is formed on the HSQ film 58 by plasma CVD or the like. Thereafter, a patterned photoresist is used to etch the second silicon oxide film 59 and the HSQ film 58 on the reflection preventive layer 55. In this way, via holes are made. Next, the photoresist is exfoliated by a treatment with oxygen plasma. The resultant is further subjected to an exfoliating treatment with an alkali-wet solution in order to remove etching remnants and the like.
As described above, at this time Sixe2x80x94H bonds in the regions of the HSQ film 58 which are exposed to the via holes and subjected to the oxygen plasma are changed into Sixe2x80x94OH bonds by the oxygen plasma treatment and the exfoliating treatment with the wet solution. Therefore, deteriorated portions 58b having an increased dielectric constant are produced in these regions. These deteriorated portions 58b cause poisoned vias.
Moreover, there is proposed a method of forming an HSQ film and subsequently subjecting the resultant to a plasma treatment with an inert gas, such as nitrogen or argon, from its surface in order to improve the strength of the HSQ film (Japanese Patent Application Laid-Open No. 8-111458).
According to this producing process in the prior art, disclosed in the above-mentioned publication, the strength of the HSQ film is improved. Thus, cracks are not easily produced even if external stress is applied to the HSQ film from a metal layer formed as an underlying layer of the HSQ film. Even by this method in the prior art, however, it is impossible to suppress the rise in the dielectric constant of the HSQ film.
An object of the present invention is to provide a semiconductor device making it possible to reduce the dielectric constant of an interlayer insulation film raised by oxygen plasma treatment or the like; and a process for producing the same.
According to one aspect of the present invention, a semiconductor device may comprise a semiconductor substrate, a wiring layer formed on the semiconductor substrate, a nitride film which covers the wiring layer, and an interlayer insulation film formed on the nitride film. The interlayer insulating film may have an opening reaching the wiring layer and containing a dielectric component represented by a chemical formula having a Sixe2x80x94H bond or a Sixe2x80x94CH3 bond.
In the aspect of this present invention, the wiring layer is covered with the nitride film. Therefore, even if a fluorine plasma treatment is conducted to lower the dielectric constant of the interlayer insulation film raised by oxygen plasma treatment in the process for producing the semiconductor device, the wiring layer is shut off from the fluorine plasma. Thus, the wiring layer is not corroded by the fluorine plasma, to obtain the interlayer insulation film having a low dielectric constant. By the reduction in the dielectric constant of the interlayer insulation film, it is possible to operate a semiconductor integrated circuit such as LSI at a high speed.
The nitride film may be made of titanium nitride or silicon nitride.
According to one aspect of the present invention, a process for producing a semiconductor device may comprise the steps of forming an interlayer insulation film containing a dielectric component represented by a chemical formula having a Sixe2x80x94H bond or a Sixe2x80x94CH3 bond on a semiconductor substrate, forming a photoresist on the interlayer insulation film, patterning the photoresist into a form of a contact hole, conducting dry-etching of the interlayer insulation film by use of the photoresist as a mask, removing the photoresist, and exposing the interlayer insulation film to nitrogen plasma and hydrogen plasma.
The step of exposing the interlayer insulation film to nitrogen plasma and hydrogen plasma may comprise the step of introducing nitrogen gas and hydrogen gas in a chamber in which the semiconductor substrate is arranged, and the volume of the hydrogen gas to the volume of the nitrogen gas may be from 2 to 80%.
According to another aspect of the present invention, process for producing a semiconductor device may comprise the steps of forming an interlayer insulation film containing a dielectric component represented by a chemical formula having a Sixe2x80x94H bond or a Sixe2x80x94CH3 bond on a semiconductor substrate, forming a photoresist on the interlayer insulation film, patterning the photoresist into a form of a contact hole, conducting dry-etching of the interlayer insulation film by use of the photoresist as a mask, removing the photoresist, and exposing the interlayer insulation film to fluorine plasma or hexamethyldisilaxane gas.
According to another aspect of the present invention, a process for producing a semiconductor device may comprise the steps of forming a wiring layer selectively on a semiconductor substrate, forming a nitride film on the entire surface, forming an interlayer insulation film containing a dielectric component represented by a chemical formula having a Sixe2x80x94H bond or a Sixe2x80x94CH3 bond on the nitride film, forming a photoresist on the interlayer insulation film, patterning the photoresist into a shape having an opening on the wiring layer, conducting of dry-etching of the interlayer insulation film by use of the photoresist as a mask, removing the photoresist, and exposing the interlayer insulation film to fluorine plasma.
In the process for the present invention, even if the dielectric constant of the interlayer insulation film is raised at the time of removing the photoresist, the interlayer insulation film is subsequently exposed to the predetermined kind of plasma or hexamethyldisilaxane gas. Therefore, the raised dielectric constant can be sufficiently lowered. As a result, a semiconductor integrated circuit such as LSI can be operated at a high speed by the drop in the dielectric constant of the interlayer insulation film.
According to the present invention, even it the fluorine plasma treatment is conducted to lower the dielectric constant of the interlayer insulation film which is raised by the oxygen plasma treatment in the process for producing the device, the wiring layer is not exposed to the fluorine plasma and is not corroded.